In a typical cellular radio network, also referred to as a wireless communication system, User Equipments (UEs) communicate via a Radio Access Network (RAN) to one or more core networks (CNs).
The user equipment is the mobile terminal by which a subscriber can access services offered by an operator's core network.
The user equipments may be mobile stations or user equipment units such as mobile telephones, also known as “cellular” telephones, and laptops with wireless capability, and thus may be, for example, portable, pocket, hand-held, computer-included, or car-mounted mobile devices which communicate voice and/or data with the radio access network.
Each cell in the cellular radio network covers a geographical area. A cell is served by Radio Base Station (RBS) equipment at a radio base station site. That is, the radio base station provides radio coverage in the cell and communicates over an air interface with user equipment units operating on radio frequencies within its range.
A radio base station is in some radio networks also called “eNB”, “eNodeB”, “NodeB” or “B node”, and will in this document be referred to as a Base Station (BS).
In some versions of the radio access network, several base stations are controlled, e.g. via landlines or radio link, by a Radio Network Controller (RNC). The radio network controller, also sometimes termed a Base Station Controller (BSC), supervises and coordinates various activities of the plural base stations connected thereto. The radio network controllers are typically connected to one or more core networks.
The cell from within which the communication between a user equipment and a base station is communicated, is referred to as the serving cell for that user equipment.
A radio link is a representation of a radio connection between a user equipment and a base station.
The radio links between the user equipments and the base stations are configured by a radio network controller. This involves assigning a user equipment identifier associated with the user equipment. In UTRAN, this user equipment identifier is associated to an uplink scrambling code that base stations may use to detect and time align a user equipment in the uplink communications. The uplink communication is the communication from the user equipment to the base station.
To support mobility of user equipments between cells in a cellular radio network, so called handovers must be performed. Handovers are necessary for example when a user equipment, such as a mobile telephone, leaves one cell and moves into another cell. Otherwise, for example an ongoing call would be dropped, due to loss of radio coverage.
A handover may be a change of serving cell, so that a user equipment being served by one cell, becomes served by another, so called candidate cell, instead.
A handover may also mean addition of a radio link to a candidate cell without removing established radio links to other cells; or replacement of one of the existing radio links by a radio link to a candidate cell. Communication that involves a multitude of cells may be referred to as macro diversity, soft handover, softer handover or coordinated multipoint, etc. The set of cells with which the user equipment have radio links is referred to as the active set.
Hence, a handover includes the setup of a radio link connection between the user equipment and the candidate cell, so that the candidate cell may become the serving cell for the user equipment. The radio links are managed by the radio network controller, which receives measurement reports from user equipments about candidate cells and based on reported information decides about additions, replacements and removals of radio links.
To enable handovers, the different cells in the cellular radio system must be identifiable. Therefore, each cell in the radio access network broadcasts a well-defined signature sequence that reveals its identity.
Some of the broadcast cell identities are reused in the radio access network, and are therefore not globally unique. In UTRAN, the reused cell identity is the downlink scrambling code, and in LTE, it is the physical cell identity.
In addition to the reused cell identities, unique cell identifiers, so called Cell Global Identifiers (CGIs), may also be broadcast from within each cell.
To discover candidate cells for handover, the user equipments may perform measurements to detect a broadcast cell identity.
To facilitate the handling of handovers, neighbor cell relations (NCR) have been introduced in many radio access networks. In a neighbor cell relation there is sufficient information about the cells in question to provide for a possible handover of a user equipment between the cells experiencing the neighbor cell relation. Such requested information may comprise for example information regarding cell identity, as well as information regarding which radio network node that is controlling the base station, serving the cell in question. For the purpose of radio network node identification, each radio network node may be associated with a unique radio network node identifier.
In UTRAN, the user equipment is, from the radio network controller it is served by, provided with a list of plausible candidate cells for handover, a so called neighbor cell list, for its current serving cell. In case the user equipment has radio links associated with multiple cells, it is provided with a neighbor cell list that the radio network controller has derived based on the neighbour cell lists of the cells in its active set.
The information needed to provide the neighbour cell lists may for example be compiled through drive tests, planning tool computations, and/or user equipment assisted measurements.
An example of the later is the Automatic Neighbor Relation (ANR) function in 3GPP LTE, where the user equipment reports both the non-unique cell identifier as well as the globally unique cell identifier upon request from serving cell.
LTE ANR is a promising feature to ensure self-configuration in the network. However, a similar feature is more difficult to introduce in other cellular radio systems, such as for example UTRAN, due to an installed base of legacy user equipments which do not support the provision of information such as for example the reporting or decoding of unique cell identities for candidate cells for handover as described above.
Moreover, user equipment measurement and/or decoding for cell identification purposes may require user equipment functionality which for cost or complexity reasons are undesirable.